Small Blue (Cupido minimus) in Ireland

Gormán beag in Gaeilge. The Small Blue, Cupido minimus, is the smallest butterfly in Ireland and a specialist of Kidney Vetch on sheltered coastal cliff, machair, and calcareous grassland.

Identify it in four steps

1. Upperside dark sooty-brown with a variable dusting of blue scales at the base, more extensive in males; not a blue butterfly in the field sense of the Common Blue.
2. Underside pale silvery-grey with fine black dots, no orange marks; the diagnostic feature when combined with size.
3. Very small: wingspan 18 to 26 mm, well under the size of the Common Blue and easy to overlook among grass.
4. Flight is a low, weak flutter close to Kidney Vetch stands, often settling on the flowers or on nearby grass heads.

Habitat in Ireland

The Small Blue depends entirely on Kidney Vetch (Anthyllis vulneraria) as its larval foodplant. It occupies sheltered coastal cliff, machair, dune grassland, and inland calcareous sites where Kidney Vetch grows in warm, low-turf conditions.

The species has a highly restricted Irish range, concentrated on the western and southern coasts. Populations are small, localised, and easily lost when Kidney Vetch stands are cut, shaded out by scrub, or heavily grazed at the wrong season.

Where to see it

• the Burren coast, County Clare: coastal grassland and machair near Fanore and Black Head support the strongest populations.
• Loop Head, County Clare: cliff-top Kidney Vetch stands hold small colonies.
• Dooaghtry and Silver Strand, County Mayo: machair and sheltered dune grassland with Kidney Vetch.

Related species

• Common Blue (Polyommatus icarus)
• Holly Blue (Celastrina argiolus)
• Small Copper (Lycaena phlaeas)